Sequestration of carbon in soil: myth or reality Jeff Baldock - - PowerPoint PPT Presentation

Sequestration of carbon in soil: myth or reality

Jeff Baldock CSIRO Land and Water Adelaide, SA

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Outline

• How much and where is organic carbon located in a soil?
• What is soil organic matter composed of and why is it important

to define its composition?

• Why would we want to increase the amount of carbon stored in

soils?

• How do we change soil carbon content through management

practices?

• What do we need to consider when measuring changes in soil
• rganic carbon?
• Issues associated with measurement
• Ground truthing results
• Economics and whole of system issues

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Where is carbon located in a soil and how much can soils hold?

0 1

Mallee sands

2 4 6

Krasnozems

0 1 2 3

Black earths 50 100 150 200 Soil Depth (cm) Soil organic carbon content (% by weight)

0 1

Red earths

2

• Pattern with depth is consistent with root distributions
• Surface soil carbon cycles faster
• Different soils hold different amounts of carbon

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

What is the soil organic carbon composed of?

Extent of decomposition increases Rate of decomposition decreases C/N/P ratio decreases (become nutrient rich) Crop residues on the soil surface (SPR) Buried crop residues (>2 mm) (BPR) Particulate organic matter (2 mm – 0.05 mm) (POC) Humus (<0.05 mm) (HumC) Dominated by charcoal with variable properties Resistant organic matter (ROC)

Soil organic carbon

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Types of soil organic carbon

Humus (HumC) Particulate material (POC) Resistant (Char) (ROC)

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Variation in amount of C associated with soil

• rganic fractions

5 10 15 20 25 30

Hamilton, Vic Hart, SA Yass, NSW Urrbrae, SA Waikerie, SA Organic C in 0-10 cm layer (Mg C/ha)

SPR BPR POC HumC ROC

Pasture Cropped Pasture Mixed rotation Mixed rotation

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Years Soil organic carbon

(g C kg-1 soil)

5 10 15 20 25 30 10 20 30 40 50 60 70 Total - TOC Conversion to permanent pasture 33 15 43

Why is it important to define the composition of soil organic carbon?

Humus Resistant - ROC Particulate - POC ~30% less humus ~800% more POC

18 y 10 y

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Vulnerability of soil carbon content to variations in management practices

Years Soil organic carbon (g C kg-1 soil)

5 10 15 20 25 30 10 20 30 40 50 60 70 TOC Humus ROC POC Conversion to intensive cultivation

18 y

Conversion to pasture

10 y

15 43 33

9 y

52

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Why would we want to increase the amount

• f carbon stored in soils?

The contributions that organic carbon makes to each function varies with:

• Composition (POC, Humus and ROC)
• Soil type (texture and mineralogy)
• biochemical energy
• reservoir of nutrients
• increased resilience

Biological roles of soil carbon

• structural stability
• water retention
• thermal properties

Physical roles of soil carbon Chemical roles of soil carbon

• cation exchange
• pH buffering
• complexes cations

Beneficial contributions that organic carbon makes to soil

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Water holding capacity (water retention)

• How much plant-available water can a soil hold
• Upper limit (wetter soil) - soil water content after

drainage

• Lower limit (drier soil) - soil water content at which

plants can no longer extract water Analogy of a sponge removed from a bucket of water

Stops dripping Upper limit Squeeze out as much water as possible Lower limit Remove sponge from water

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Change in water holding capacity with a 1% increase in soil organic carbon content

For 0-10 cm layer of South Australian Red-brown earths 3 mm extra stored rainfall for 10 rainfall events equates to 30 mm total Issue: harder to build up soil carbon on a sandy soil than a clay

y = -0.1229x + 5.5029 R2 = 0.82

1 2 3 4 5 6 10 20 30 40 Clay content (% of soil mass) Change in water holding capacity (mm water) Sandy soils ~5 mm Clay loams ~2 mm Average ~3 mm

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

3) increase C stored in one or all soil components CO2 Plant production Photosynthesis Resistant

• rganic C

Burning or Biochar production Death

The carbon cycle: options for sequestering carbon

Residues Particulate

• rganic C

Humus

• rganic C

Increasing extent of decomposition Carbon sequestration options Harvested products Harvest Decomposition 1) increase C stored in long lived plants 2) increase C stored in long lived products Decomposition Soil animals and microbes Death 4) mover more carbon into resistant forms (e.g. charcoal)

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

What determines soil organic carbon content?

Soil organic carbon content Inputs of

• rganic carbon

Losses of

• rganic carbon

= ,

f

Inputs

• Net primary

productivity (return of residues)

• Addition of waste
• rganic materials

Losses

• Conversion of
• rganic C to CO2
• Protection offered

by soil minerals

• Extent and

frequency of cultivation

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Years Soil organic carbon

(g C kg-1 soil)

5 10 15 20 25 30 20 40 60 80 100 120 140

Balance between inputs and outputs

Inputs x 2 Inputs x 3 Inputs / 2 Inputs / 3 Inputs = Outputs

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Years Soil organic carbon

(g C kg-1 soil)

5 10 15 20 25 30 20 40 60 80 100 120 140

Influence of variations in climate and management

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Minimum requirements for tracking soil

• rganic carbon for accounting purposes
• 1. Collection of a representative soil sample to a minimum

depth of 30 cm

• 2. An accurate estimate of the bulk density of the sample
• 3. An accurate measure of the organic carbon content of a

soil sample For 0-30 cm soil with a bulk density of 1.0 Mg/m3 and a carbon content of 1.0% = Mass of Carbon (Mg C/ha) Depth (cm) 30 Mg C/ha x Bulk density (g/cm3) x Carbon content (%) =

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Dynamic nature of SOC and its fractions

8 16 24 32 1/6/98 6/2/99 14/10/99 20/6/00 25/2/01

Date of sample collection Amount of organic C

(Mg C ha-1in 0-10 cm)

POC Humus ROC TOC

Irrigated Kikuyu pasture – Waite rotation trial

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Soil bulk density (Mg/m3) 1.1 1.2 1.3 1.4 Management induced compaction

Correcting soil carbon for management induced changes in bulk density

Original soil surface Mass Soil 0-30 cm (Mg/ha) 3300 3600 3900 4200 Depth for equivalent mass (cm) 30.0 27.5 25.4 23.6 Original 30 cm depth New 30 cm depth Organic C loading (Mg/ha) 1% OC, no BD correction 33 36 39 42 1% OC, with BD correction 33 33 33 33

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Influence of tillage on changes in soil carbon with depth

If red region > blue region = sequestration For 0-10 cm layer red region > blue region (sequestration) For 0-30 cm layer red region = blue region (no sequestation) Cultivated to 10 cm Uncultivated Organic carbon content (% soil mass) Soil depth (cm) 0.0 0.5 1.0 1.5 2.0 2.5 10 20 30 40 50 60 70 80

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Ground truthing claims: the carbon perspective

10 20 30 40 50 60 70 80 90 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7

Bulk density (g/cm3) Amount of carbon in the 0-10 cm layer (Mg C/ ha)

1% SOC 2% SOC 3% SOC 4% SOC

24 48 Changing soil carbon from 2% to 4% over 5 years Amount of C required: 24 Mg C 50 Mg Dry Matter (DM) Rate per year (no losses): 10 Mg DM/y 50% allocation below ground equates to 5 Mg shoot DM/y Rate per year (with 50% loss) 20 Mg DM/y (50% loss) 50% allocation below ground 10 Mg shoot DM/y

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

100 200 300 400 500 600 1.0 1.2 1.4 1.6

Bulk density (g cm-3) Amount of P (kg/ha)

1.0% SOC 2.0% SOC 3.0% SOC 4.0% SOC

C/P=120

Ground truthing claims: the nutrient perspective

1000 2000 3000 4000 5000 6000 7000 1.0 1.2 1.4 1.6

Bulk density (g cm-3) Amount of N (kg/ha)

1.0% SOC 2.0% SOC 3.0% SOC 4.0% SOC

2400 4800 200 400

C/N=10

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Modelling changes in soil carbon content

1982 1987 1992 1997

Year

10 20 30 40 50 60 70

0-30 cm Soil C (t/ha)

DPM RPM HUM IOM BIO Soil

Modeled

POC HUM CHAR TOC

Measured

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Modelling changes in soil organic carbon under permanent pasture at Nimmitabel

Model conditions

• Location: Nimmitabel, NSW
• Annual rain 695mm,
• Apr-Oct rain 380mm
• Dry Matter production
• 6 t shoot dry matter
• 50% of shoot dry matter ingested
• 67% of ingested carbon lost
• root/shoot ratio = 1
• Soil properties
• 0-30 cm soil layer
• bulk density = 1.4 Mg/m3
• clay content = 15%

30 60 90 120 150 180 Jan Mar May Jul Sep Nov Month of the year mm Water Rain Pan Evap

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Potential changes in 0-30 cm soil carbon content (t C/ha) at Nimmitabel

40 80 120 160 200 100 200 300 400 500 Years since start of simulation Amount of soil organic carbon (t C/ha for 0-30 cm layer) 4 t shoot dm/ha 6 t shoot dm/ha 8 t shoot dm/ha 3.94 2.96 1.97 Soil Carbon % 0-10 cm

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Predicted change in soil carbon over 20 years and potential $ value

Shoot dry matter (t/ha) Initial soil carbon (tC/ha) Soil carbon @ 20 y (tC/ha) Change in soil carbon (tC/ha) Average change (tC/ha/y) Annual value @$25/tC ($/ha) 2.0 138 115

• 23
• 1.11

$ -28.37 4.0 138 127

• 11
• 0.55

$ 13.75 6.0 138 138 $ 0.00 8.0 138 149 11 0.55 $ 13.75 10.0 138 161 23 1.11 $ 28.37

• Analysis only considers change in soil carbon
• Need to consider other emissions and production costs

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Management options for increasing soil carbon content

• Principal: increase inputs of carbon to the soil
• Maximise capture of CO2 by photosynthesis and addition of

carbon to soil

• Options
• Maximise water use efficiency (kg total dry matter/mm water)
• Maximise stubble/residue retention
• Introduction or increased perennial components (where

appropriate)

• Alternative crops - lower harvest index
• Alternative pasture species – increased below ground allocation
• Addition of offsite organic materials – diversion of waste streams

Relationship between commodity prices and value of carbon will be a defining factor

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Considerations when looking at entering soil carbon into a carbon trading scheme

• Biophysical constraints
• Availability of water
• Variations in soil type
• Previous land use

Not all locations offer the same potential for additional C capture in soil

• Economic – farmers are paid for product, breeding programs

are attempting to maximise carbon capture and removal in products

• World food security – do we have an obligation?
• Permanency of increase
• All carbon entered must be maintained
• Potential reduction in management flexibility in the future
• Implications on land value

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

$$ for C sequestration – fact or fiction

• There is no doubt that Australia soils could hold more

carbon

• Challenge – increase soil C while maintaining economic

viability and increasing global food supply

• Options do exist:
• Particularly where intensive cropping systems have been used
• Options for soils under pasture will be more limitted
• Options must be tailored to soil and climatic conditions
• Under current C trading prices
• Difficult to justify managing for soil C on the basis of C

trading alone

• Do it for all the other benefits enhanced soil carbon gives:

water holding capacity, nutrient cycling, stabilisation of structure, protection against erosion, etc.

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Take home messages

• Organic matter contributes positively to many soil properties
• Different soils can hold different amounts of organic matter
• Management can alter the amount and distribution of different

types of organic matter

• Measuring changes in soil organic carbon requires careful

consideration

• Options to increase carbon must be tailored to the local

conditions and economic considerations of the farmer

• CSIRO. Monaro Farming Systems – Carbon Forum 6/07/2009

Thank you

CSIRO Land and Water Jeff Baldock Research Scientist Phone: +61 8 8303 8537 Email: jeff.baldock@csiro.au Web: http://www.clw.csiro.au/staff/BaldockJ/ Acknowledgements Jan Skjemstad, Evelyn Krull, Jon Sanderman, Lynne Macdonald, Ryan Farquharson, Steve Szarvas, Leonie Spouncer, Athina Massis Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: Enquiries@csiro.au Web: www.csiro.au